Epithelial ovarian cancer is the most common gynecologic malignancy and the sixth most common cancer in women, causing 125,000 deaths yearly. (Cannistra S. A., Cancer of the ovary, N Engl J Med, 2004; 351:2519-29) The survival rate at five years after initial diagnosis is only 30% due to the late stage diagnosis for greater than 70% of ovarian cancers. When ovarian cancer is diagnosed in its early stages (e.g. still organ confined), the survival rate at five years exceeds 90%. However, only 19% of all ovarian cancers are diagnosed at the early stage. (Feely K. M. et. al., Precursor lesions of ovarian epithelial malignancy, Histopathology, 2001; 38:87-95) Ovarian cancers occur as four major subtypes: serous, mucinous, endometrioid, and clear cell. Each of these histologic types is associated with distinct molecular and morphologic genetic alterations. (Bell D. A., Origins and molecular pathology of ovarian cancer, Mod Pathol, 2005; 18 Suppl 2:S19-32)
MicroRNAs (miRNAs) are a class of 22-nt noncoding RNAs, which are evolutionarily conserved and function as negative regulators of gene expression. Like conventional protein-coding mRNA, miRNAs are transcribed by RNA polymerase II, spliced and polyadenylated (called primitive miRNA or pri-miRNA). However, unlike mRNA, the pri-miRNAs contain a stem-loop structure that can be recognized and excised by the RNAi machinery to generate hairpin ‘precursor’ miRNAs (pre-miRNA) that are, ˜70 nt in animals or ˜100 nt in plants. Pre-miRNAs are cleaved by the cytoplasmic RNase III Dicer into a ˜22-nucleotide miRNA duplex: one strand (miRNA*) of the short-lived duplex is degraded, whereas the other strand serves as a mature miRNA. The mature miRNA then guides a complex called miRNP (miRNA-containing ribonucleo-protein particles) to the complementary site(s) in the 3′ untranslated region (UTR) of a target mRNA. Consequently, translation blockade or mRNA degradation will occur depending on whether it is partially matched or completely matched with the target genes, respectively (Lagos-Quintana, et al., Identification of novel genes coding for small expressed RNAs. Science 2001; 294:853-8). Moreover, the levels of individual miRNAs are dramatically changed in different cell types and different developmental stages, suggesting that miRNA plays a role in cell growth, differentiation, and programmed cell death (Lagos-Quintana, et al., 2001; Bartel, D., MicroRNAs: genomics, biogenesis, mechanism, and function. Cell 2004; 116:281-97).
miRNAs have been shown to be aberrantly expressed or mutated in human cancer, indicating that they may function as a novel class of oncogenes or tumor suppressor genes (Calin G A, et al., Frequent deletions and down-regulation of micro-RNA genes miR15 and miR16 at 13q14 in chronic lymphocytic leukemia. Proc Natl Acad Sci USA 2002, 99:15524-9; Zhang, L., et al., microRNAs exhibit high frequency genomic alterations in human cancer. Proc Natl Acad Sci USA. 2006, 103:9136-41; Lu, J., et al., MicroRNA expression profiles classify human cancers. Nature 2005, 435:834-8; Chan, J., et al., MicroRNA-21 is an antiapoptotic factor in human glioblastoma cells. Cancer Res. 2005; 65:6029-33; Takamizawa, J., et al., Reduced expression of the let-7 microRNAs in human lung cancers in association with shortened postoperative survival. Cancer Res 2004; 64:3753-6; He, H., et al. The role of microRNA genes in papillary thyroid carcinoma. Proc Natl Acad Sci USA 2005; 102:19075-80). The first evidence of involvement of miRNAs in human cancer came from molecular studies characterizing the 13q14 deletion in human chronic lymphocytic leukemia, which revealed two miRNAs, miR-15a and miR-16-1 (Calin G A, et al., 2002). Subsequently, miRNA deregulation was detected in other human malignancies, including breast carcinoma (Iorio, M. et al., MicroRNA gene expression deregulation in human breast cancer. Cancer Res. 2005; 65:7065-70; Zhang, L., et al., 2006), primary glioblastoma (Lu, J., et al., 2005; Chan, J., et al., 2005), lung cancer (Takamizawa, J., et al., 2004), papillary thyroid carcinoma (He, H., et al., 2005), colon carcinoma (Volinia, S., et al., A microRNA expression signature of human solid tumors defines cancer gene targets. Proc Natl Acad Sci USA. 2006, 103:2257-61.) and pancreatic tumors (Lee, E., et al., Expression profiling identifies microRNA signature in pancreatic cancer. Int J Cancer. 2007, 120:1046-54; Gaur, A., et al., Characterization of microRNA expression levels and their biological correlates in human cancer cell lines. Cancer Res. 2007, 67:2456-68). For instance, the miR-17-92 cluster is upregulated in B-cell lymphomas and lung cancer. miR-143 and -145 are down-regulated in colon carcinomas. A decrease in Let-7 is detected in human lung carcinomas and restoration of its expression induces cell growth inhibition in lung cancer cells (Johnson, S., et al., RAS is regulated by the let-7 microRNA family. Cell 2005, 120:635-47). The BIC gene, which contains the miR-155, is up-regulated in some Burkitt's lymphomas and several other types of lymphomas (Metzler, M., et al., High expression of precursor microRNA-155/BIC RNA in children with Burkitt lymphoma. Genes Chromosomes Cancer 2004, 39:167-9; Eis, P., et al., Accumulation of miR-155 and BIC RNA in human B cell lymphomas. Proc Natl Acad Sci USA 2005, 102:3627-32).
A number of miRNAs were observed deregulated in human ovarian cancer. The deregulation of miRNAs refers to the upregulation or down-regulation of the expression of the specific miRNAs. The aberrant expression of miR-214, -199a*, -200a and -100 was detected in nearly half or over half of ovarian cancers, especially in late stage and high grade tumors. Significantly, miR-214 was demonstrated to negatively regulate PTEN by binding to its 3′UTR leading to inhibition of PTEN translation and activation of Akt pathway. As a result, miR-214 induces cell survival and cisplatin resistance, which were overridden by either small molecule Akt inhibitor or expression of PTEN cDNA lacking 3′UTR